The major goal of the Clinical Core is to serve as a resource for the Neuropathology Core and Center Projects #1-4 and facilitate investigations at Johns Hopkins Medical Institutions and collaborating institutions that require subjects with well-characterized Parkinson's disease (PD) and/or postmortem brain tissue. The Specific Aims are: 1. To conduct longitudinal clinical assessments of individuals with idiopathic PD and age-matched controls. Clinical characterization will involve comprehensive assessments of motor, cognitive, and psychiatric status with longitudinal follow-up until death. These data will facilitate clinicopathological correlations in conjunction with the Neuropathology Core and independent clinical research studies. 2. To maintain and expand a Brain Donation Registry for enrollment of individuals with idiopathic PD and related disorders and age-matched controls who are willing to donate their brain for research purposes after death, thereby providing material for the Neuropathology Core, studies requiring human brain tissue in Projects #1-4, and studies on clinicopathological correlations. 3. To provide the fundamental infrastructure for clinical research on PD that facilitates independently funded clinical investigations of PD at JHMI and collaborating institutions. 4. To train physician-scientists in the clinical assessment and management of patients with PD and related disorders and in the performance of clinical research on PD. Characterization of both motor and non-motor features of PD, their relationships, and their progression over time has implications for identifying clinicopathological correlations and pathophysiological processes that contribute to different etiologies, therapeutic response, and prognosis. Brain tissue from patients with well-characterized clinical features is essential to research on underlying disease mechanisms in PD.